This week I searched through the 21st century skills map for all content areas and I came across a section on critical thinking and problem solving for physical science. This essentially is the "main idea" for what students should be able to do in physical science through critical thinking.

--> Critical Thinking and Problem Solving
Student groups in a physical science class design experiments to examine how different sources of error can impact the results of a lab activity focused on the relationship between force, mass, and acceleration. 
Retrieved by: www.p21.org/storage/documents/21stcskillsmap_science.pdf

I believe that students need to become critical thinkers and be able to ask higher order questions to really be apart of a 21st century skill science classroom. The ability to use creativity and innovation to learn a science concept is where science classrooms should go.  

Through my searches I also found a cool website for students where they can use their engineer hat and design. Students follow the whole website from start to finish learning physical science and creating!! This gives them real world application to what they learn in the classroom and when they go to an amusement park maybe they will have some cool things to share with their families!
Check this out:
http://www.learner.org/interactives/parkphysics/

The only challenge I would face is time in my classroom. The time to discover and keep up with the curriculum. I struggled with that this year and fell a little behind. I need to better work on the timing of everything for next year!